Floyd Mayweather and Conor McGregor stare down each other at their London press conference

Ireland's first UFC belt holder came face-to-face with his upcoming opponent for the fourth time in as many days last night at the SSE Wembley Arena in London, England.

Just like their previous encounters, the two biggest names in combat sports traded verbal jabs with one another, to the delight of the Irish-laden crowd.

McGregor, who was celebrating his 29th birthday, was on top form in his final showdown with the Olympian, taunting him over a whole host of subjects.

But his best joke came moments after Mayweather took a selfie with the London hostile crowd.

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"Mate, you're 40. Get that f****** phone out of your hand like you're a kid," the reigning UFC lightweight champion said.

"He was wearing high heels yesterday. Check to picture from yesterday and check it from the day before, proper high heels that b**** was wearing.

"You should have wore them on the first day you stupid baldy t***."

“You should have wore them on the first day you stupid baldy t***”

Conor McGregor on Floyd Mayweather

A fired up McGregor then went on to reiterate his belief that he will shock the world and hand Mayweather his first professional defeat.

"I do what I do," 'The Notorious' said. "I am going to sleep this man inside of four rounds. The same way I sleep them every other time."

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Floyd Mayweather and Conor McGregor's final encounter got rather heated

Mayweather, 40, returned fire by repeatedly labelling McGregor a 'bitch'. And to the shock of the packed-out arena, the legendary boxer called his 50th professional opponent a 'microwave meal'.

"Dana - me and you got the most money. Keep pimping this b****. Twenty-one years ago, me and you had a game plan," he said.

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Conor McGregor has vowed to KO Floyd Mayweather

"We're the smart ones. We were going to take these foreign fighters and we were going to use them. We are some smart Americans and you're out here with a quitter but I forgot: you're the pimp and this is your h**.

"You're a microwave meal with a cheap-ass watch on - step your game up."